We report a case of a 59-year-old woman who had severe metabolic acidosis and hypokalemia due to an enterovesical fistula. The patient came to our hospital complaining of systemic weakness and numbness of the fingers. She was found to have hyperchloremic metabolic acidosis (arterial bicarbonate, 2.8 mEq/l) and hypokalemia (serum potassium, 1.9 mEq/l) and was admitted for treatment. Following the correction of metabolic acidosis and hypokalemia, the patient was examined for the underlying cause of these electrolyte and acid-base disorders. She had a history of total hysterectomy followed by radiotherapy due to uterine cancer 30 years previously. After the surgery, she had suffered postoperative neurogenic bladder dysfunction, necessitating intermittent self-catheterization. Two years before admission, she had begun to experience watery diarrhea. A radiographic study after recovery from the acid-base and electrolyte disorders revealed the presence of an enterovesical fistula. The fistula was surgically resected and the metabolic acidosis completely cleared. Unexplained hyperchloremic metabolic acidosis with hypokalemia may suggest the presence of an enterovesical fistula in patients with a surgical history of malignant pelvic tumor and neurogenic bladder dysfunction.